Wire-woven Bulk Kagome Research Articles

The effects of geometrical topology on fluid flow and thermal performance in Kagome cored sandwich panels

This study presents a systematic comparison of overall and local flow characteristics and heat transfer between two sandwich panels with single-layered Kagome and wire-woven bulk Kagome (WBK) cores under an identical porosity. Simulations are performed in the Reynolds number range of 3995–8710 by a verified SST turbulence model. The results reveal that the Kagome sandwich panel exhibits a 26–31% higher overall Nusselt number relative to the WBK sandwich panel with similar pressure drop, though the area-averaged Nusselt number on the ligaments of the Kagome panel is about 42% lower than that of the WBK panel. This is attributed to more high-momentum vortices and higher turbulent kinetic energy near the endwall in the Kagome panel compared to the WBK panel. This research indicates that the geometrical topology inside sandwich panels is important to induce stronger vortex flow close to heated endwalls for improving endwalls heat transfer behavior and overall thermal performance.

A weaving machine for three-dimensional Kagome reinforcements

Two-dimensional or three-dimensional (3D) textiles have been used as reinforcement in composite materials. Most techniques for weaving 3D textiles have been developed to obtain a compact preform so that the final product, the fiber-reinforced composite, has a high volume fraction of fibers with the least fraction of matrix for high strength. Contrarily, this article describes a novel technique for weaving a loose 3D preform called wire-woven bulk Kagome with polymer wires or threads. Firstly, the principle is explained by using a manual loom. A weaving machine is then designed with detailed mechanisms and its prototype is presented. Finally, the benefit, shortcomings, and future plans are discussed.

Seismic Strengthening Effects Based on Pseudodynamic Testing of a Reinforced Concrete Building Retrofitted with a Wire-Woven Bulk Kagome Truss Damper

A passive damper with a wire-woven bulk Kagome truss design was recently developed; its applicability as a passive damper to improve the seismic performance of building systems, including shear hysteresis behavior, energy dissipation capacity, and fatigue, was confirmed by material tests. The Kagome truss, a periodic cellular metal type, is composed of evenly distributed helical wires with a constant pitch and helical radius in six directions. The purpose of this study was to develop a new passive damper system for seismic strengthening of existing reinforced concrete (RC) frames. The proposed external connection methodology uses a wire-woven bulk Kagome truss (i.e., a Kagome damper external connection (KDEC) system), to dissipate earthquake energy using the dynamic interaction among an existing building, a support structure, and the Kagome damper installed between them. Four test specimens were designed and then strengthened with the KDEC system. Cyclic loading and pseudodynamic tests were conducted; lateral load-carrying capacity, deformation, and hysteresis characteristics were investigated, as well as the maximum response strength, response ductility, and earthquake damage degree, and compared to a control sample. Test results revealed that the KDEC system effectively dissipated the earthquake energy, showing considerable resilience under large-scale earthquake conditions.

Experimental Investigations of Natural Convection in Wire-Woven Bulk Kagome

Natural convection in an open and highly anisotropic cellular material, wire-woven bulk Kagome (WBK) is experimentally characterized. A series of pressure drop and heat transfer experiments are conducted. In particular, effect of inclination angle on the heat transfer rate for porous-cored heat sinks (WBK and metallic foams), as well as smooth plate was experimentally investigated. There exists an optimal inclination angle for smooth plate and porous-cored heat sinks in association with the maximum heat transfer rate (Nusselt number). An advance in optimal inclinational angle was observed in porous media during the full inclination angle range from \(0^{\circ }\) (horizontal) to \(90^{\circ }\) (vertical) due to the enhanced lateral conduction and a further advance was found in WBK specimen. A strong anisotropic heat transfer existed in terms of different orientations of WBK specimen: O-B orientation with a bigger cross-sectional surface area density (blockage ratio) reveals a higher heat transfer rate than O-A orientation. Further, in comparison with isotropic metallic foams with a given porosity, the WBK which is positioned at vertical orientation can dissipate more heat than the foams due to the higher permeability resulting from less pressure drop in the WBK formed by an assembly of cylindrical wires.

Effects of Gaps between Discontinuous Wire Woven Kagome Cores upon Bending of Sandwich Panels

WBK (Wire-woven Bulk Kagome) is a periodic cellular metal assembled of helical wires. The mechanical behavior under compression or shear, optimal design of a sandwich panel with WBK core, and characteristics of heat dissipation media have been studied, which proves feasibility of WBK as core material with multi-function capability. When WBK is used as the core material in a large scale sandwich panel, gaps between discontinuous cores are inevitable in their fabrication or building even larger scale structures using them. In this study, the effects of the gaps on mechanical behavior of sandwich panels are investigated. Theoretic analysis, experiments with three-point bending, and numerical analyses are performed to predict the strength and to analyze the results

Effective thermal conductivity of wire-woven bulk Kagome sandwich panels

Thermal transport in a highly porous metallic wire-woven bulk Kagome (WBK) is numerically and analytically modeled. Based on topology similarity and upon introducing an elongation parameter in thermal tortuosity, an idealized Kagome with non-twisted struts is employed. Special focus is placed upon quantifying the effect of topological anisotropy of WBK upon its effective conductivity. It is demonstrated that the effective conductivity reduces linearly as the porosity increases, and the extent of the reduction is significantly dependent on the orientation of WBK. The governing physical mechanism of anisotropic thermal transport in WBK is found to be the anisotropic thermal tortuosity caused by the intrinsic anisotropic topology of WBK.

Buckling of WBK Cored Sandwich Panels under Longitudinal Compression

Bucking behaviors of WBK (Wire-woven Bulk Kagome) cored sandwiches under longitudinal compression are studied. Slender and short specimens are fabricated of mild steel wires and face sheets, and are fixed through copper brazing. And buckling experiments with axial compression are carried out. The failure mechanisms are analyzed by the theory and numerical simulation. Effects of eccentricity of loading or geometry, and fixings at both ends are investigated. Practical and physical meanings of the results and potential of WBK as a sandwich core are discussed.

Compressive Strength of Wire-woven Bulk Kagome with Various Orientations

To date, the mechanical behavior of WBK under compression has been studied for a certain orientation in which WBK is presumed to have the highest strength. In this study, the compressive strength of WBK various orientation are presented. First, analytic solutions are derived with consideration of wire waviness and brazed joints at the cross points among wires. Numerical simulations are performed with a unit cell model with periodic boundary conditions. Compressive strengths depending on the orientation estimated by the approaches are compared with experimental results on failure maps to prove the validity. Practical and physical meanings of the results are discussed.

Bending response of sandwich panels with discontinuous wire-woven metal cores

The effects of a gap between discontinuous WBK (Wire-woven Bulk Kagome) cores on the bending properties of mild steel sandwich panels were elaborated. Analytic solutions were derived, and the experimental and numerical results of the bending response of sandwich panels with continuous and discontinuous WBK cores were presented. The analytic solutions of sandwich panels with continuous or discontinuous WBK cores under bending load provided good estimations of the failure mode, peak load, and bending stiffness in comparison with the experimental results. The strength and stiffness of sandwich panels with discontinuous WBK cores under bending load often substantially deteriorated depending on the gap width between the cores and on the detailed geometry near the gap. The analytic solutions successfully explained how the deterioration of the bending strength or stiffness could be minimized, when two separate sandwich panels or cores are to be joined.

Effects of cell size and orientation on compressive strength of WBK

This article presents the mechanical properties of mild steel WBK (Wire-woven Bulk Kagome) cores under compression. A method to measure precisely the average displacements of specimens is described. And analytic solutions of the equivalent strength and Young’s modulus are introduced. The equivalent peak strengths of the WBK cores in y and x-orientations were about 3/4 and 1/2 of that in z-orientation, respectively, and the equivalent Young’s moduli in y and x-orientations were about 5/6 of that in z-orientation. Regardless of the orientation or cell size, the measured equivalent peak strengths were always higher than those estimated by the analytic solutions which were modified taking into account the curved struts and the brazed joints among the wires. On the other hand, the measured equivalent Young’s moduli were often somewhat lower than those estimated by the corresponding equations modified accounting for the realistic geometry of WBK, because of the combined rotations of the small, triangular structures composing the in-plane meshes and the out-of-plane, helically-curved struts in the WBK cores.

In-plane compression response of wire-woven metal cored sandwich panels

This article presents the buckling behaviors of two types of WBK (Wire-woven Bulk Kagome) cored sandwich panels subjected to in-plane compression. Classical theories are introduced, and the experimental and numerical results are presented. The effects of several design parameters are analyzed. For both types, the peak loads were governed by macroplastic buckling. Low shear modulus and strength of the WBK core substantially influenced the buckling behaviors of the sandwich panels before and after their peaks. A small initial deflection greatly decreased the resistance against buckling of the sandwich panels with thinner cores, as confirmed by a two-stage FEA (Finite Element Analysis) and the analytic solution accounting for eccentricity.

Equivalent material properties of a wire-woven cellular core

New analytic solutions are derived for the relative density, equivalent strength under compression and equivalent Young’s modulus of WBK (wire-woven bulk Kagome). The three dimensional curvature of struts and the considerable size of the brazed filler metal joining the struts are unique to a wire-woven structure and therefore, must be taken into account. The solutions are verified by comparison with the results of CAD models and finite element analysis as well as with experimental data. The effects of the slenderness ratio of struts, the size of the brazed joint, and the hardening exponent of the wire material are investigated. Sources of the discrepancy with the experimental results, limits in application, and engineering significance are discussed.

A new fabrication method to improve metal matrix composite dispersibility

A new type of periodic cellular metal called wire-woven bulk Kagome (WBK) was used as a precursor for creating the composite materials with improved dispersibility. Preheated and non-preheated preforms were placed into molds, and then molten aluminum was poured into them to fabricate composites. The effects of preheating on the wettability and interfacial reaction between the aluminum matrix and the WBK preform were then investigated. The preheated preform composite had good wettability compared to the non-preheated preform composite. Interfacial phenomena between the aluminum matrix and the WBK preform were observed. Our research offers a new avenue for solving the problem of composite material dispersibility.

Thermomechanical Properties of Brazed Wire-Woven Bulk Kagome Cellular Metals for Multifunctional Applications

This paper presents a combined experimental and theoretical study on the fundamental thermomechanical properties of high-porosity, wire-woven bulk Kagome (WBK) cellular cores fabricated using a newly developed technique. Particular focus is placed upon the influence of brazing on the strength, forced air convection characteristics, and effective thermal conductivity of thematerial. Upon uniaxial compressive loading, brazing of the WBK joints increases the core strength more than 10 times compared with that without brazing. Thermally, althoughbrazinghas no effect on the effective thermal conductivity, it leads to significantly enhanced heat dissipation under forced convection. In the absence of fluid flow, heat spreading along the lateral ligaments plays no part in conduction, whereas the tortuous ligaments along the direction of conduction act to reduce the effective conductivity. However, under forced convection, the activation of convection from the lateral ligaments as a result of brazing leads to pronounced enhancement of the overall heat dissipation capability.

Forced convective heat transfer in all metallic wire-woven bulk Kagome sandwich panels

This experimental study reports on forced convective heat transfer in a highly porous cellular material, wire-woven bulk Kagome (WBK), made of aluminum (Al) helix wires forming Kagome-like unit cells that are distributed periodically and sandwiched between two solid Al facesheets. Due to the topological anisotropy of the WBK, two orientations, the most open and closed orientations, were selected for pressure drop and heat transfer measurements. For the range of Reynolds numbers ( Re) considered, the pressure drop in the WBK was found to be skin friction dominated at low Re (laminar flow regime; no orientation effect on pressure drop) and form dominated at high Re (transition from laminar to turbulent flow regime; slightly higher pressure drop in the most closed orientation). For heat transfer across the WBK, the Nusselt number in the most closed orientation was consistently higher than that in the most open orientation, attributable mainly to the difference in the open area ratio of the two orientations.

Mechanical behaviour of tube-woven Kagome truss cores under compression

Wire-woven bulk Kagome (WBK) has recently been used to fabricate multi-layered truss-type cellular metals. A tube WBK structure is fabricated of tubes instead of solid wires. In this work, tube WBK specimens with various combinations of slenderness ratio and inner-to-outer diameter ratio of the tubular struts were tested under compression to investigate the effects of geometric factors on peak strength, equivalent Young′s modulus and energy absorption capability. To aid in the physical interpretation of the results and the development of a design methodology, numerical simulations of single tubular struts were performed with a wide range of slenderness ratio and inner-to-outer diameter ratio. The tube WBKs outperformed most cellular metals, but they were inferior to hollow trusses, especially those with a diamond configuration. However, energy absorption of the tube WBKs was comparable to that of hollow trusses because of stable deformation of the tube WBKs after initial yielding or maximum strength.

New Cellular Metals with Enhanced Energy Absorption: Wire‐Woven Bulk Kagome (WBK)‐Metal Hollow Sphere (MHS) Hybrids

AbstractTwo types of new cellular metals are fabricated by assembling layer by layer helically‐formed wires with metal hollow sphere (MHS) arrays. In the finished configuration, the MHSs are located in small tetrahedrons or octahedrons of the inner space of a wire‐woven bulk Kagome (WBK) structure. Compression tests reveal excellent energy absorption, which is attributed to combination of suppression of strut buckling in the WBK and moving plastic hinge occurring in the MHSs. The WBK‐MHS hybrids outperform competitors in deformation energy absorption.

초경량 금속 구조재 직조장치의 설계 및 제작

와이어직조 카고메(WBK)는 나선형으로 성형된 와이어를 6 방향에서 조립하여 제작된다. 지금까지의 WBK 는 수작업으로 조립되어 왔지만, 산업적 적용을 위해서는 조립공정의 자동화가 필수적이다. 또한, 유연한 와이어로 WBK 를 제작할 경우 기하학적 형상을 유지할 수 없으므로 직조기와 같은 자동화 기계의 개발이 절실하다. 이번 연구에서는, 유연한 와이어를 이용하여 WBK 를 제작하는 직조기를 설계 및 제작하였다. 이 직조기는 상부 플레이트의 회전운동과 와이어를 삽입하는 장치의 병진운동으로 작동된다. 그리고 이미 삽입된 와이어 간의 간섭을 방지하기 위한 빗살장치는 다층의 카고메망 사이에 위치된다. 또한 이 직조기는 나선형 와이어와 직선형 와이어로 구성된 semi-WBK 의 제작에도 이용될 수 있다.

Taguchi method-based sensitivity study of design parameters representing specific strength of wire-woven bulk Kagome under compression

Abstract Wire-woven bulk Kagome (WBK) is a new truss-type cellular metal fabricated by assembling helically-formed wires. In this work, the main design parameters governing the compressive strength of WBK were selected from various geometric and material factors. The Taguchi method was used to minimize the number of experiments required to evaluate the sensitivity of each design parameter with the specific compressive strength of WBK. As numerical experiments, finite element analyses were performed to investigate the mechanical responses of WBK with various combinations of levels for selected design parameters. We found that the slenderness ratio is the dominant and most influential design parameter characterizing the specific strength of WBK, followed by the strain-hardening exponent and the yield strength of the brazed filler metal. The height of the braze normalized by the wire diameter is the least influential design parameter. In addition, an optimized design for the highest specific strength of WBK was derived.

A parametric study on compressive characteristics of Wire-woven bulk Kagome truss cores

Abstract Compressive behaviors of the Wire-woven bulk Kagome (WBK) cores fabricated of stainless wires are experimentally investigated. Effects of geometrical parameters such as the wire diameter, strut length and number of layers on the compressive behaviors are studied. Also, behaviors of two different types of the specimen configurations, namely, pointed faced and flat faced specimens are compared to each other and analyzed. As the number of layers increases, the strength of the specimens slowly decreases. The compressive strength of WBK dominantly depends on the slenderness ratio. Difference in the specimen configurations results in the significant difference of the stress–strain responses for the specimens with slenderness ratio higher than a certain value. The compressive strength and energy absorption capability of WBK are as good as those of the regular truss type cellular metals, when the relative density is sufficiently high.